You need save only one bridge undestroyed. Defend it with walls from the both side (i prefer western bridge). AI is stupid enough - imperials will try to destroy bridge, not walls
Pair of turrets will deal with them shortly. Also imperials will try to destroy command center in southern village - defend it with walls & 2-3 turrets. I hold Echuu, the Jedi, in on of the turrets. When imperials attacks, he convert one of their stormtroopers & i garrisoned it in one of the turrets. After 10-15 attacks you will have full garrison!
I built all production structures (command center, troop center & and so on) at the start point of the game. Imperials wouldn't attack it!
When you build 7-10 mounted troops, you can attack imperial outpost at the north - it's poor defended. For the victory you must destroy ONLY ONE outpost from two.